The present invention relates to an electrode in the form of a wire or a rod for machining a piece by electro-erosion, comprising a metallic core and a cladding constituted by at least one other metal.
Such an electrode is described in the document JP 1-78724. It comprises a brass core and a cladding of pure manganese of a thickness of about 1 xcexcm. This electrode permits obtaining precise finishing machining. During rough machining, the cladding is adapted to be completely eliminated from the surface of the wire and thus does not lead to improvement of the machining. When it is sought to obtain greater thicknesses of the manganese layer, the latter gives to the wire too great a rigidity and hardness, which gives rise to problems during production of the wire and prevents good drawing of the wire. Moreover, given that the manganese deposited by electrolysis is in a metastable phase, its surface condition degrades and its adherence to the core decreases with time.
The present invention has for its object to overcome these drawbacks, and the invention is characterized to this end by the fact that the cladding is constituted by at least one deposit of an alloy comprising manganese and at least one second metal selected from the group of metals comprising Zn, Co, Cu, Ag, Fe, Mo, Ni, Se, Sn, W, the deposit having a proportion of manganese comprised between 5 and 85% by weight and a thickness greater than 1 micrometer.
The second metal, in particular zinc, permits obtaining a wire whose external layer is much more easily deformable. There can thus be produced drawn wires whose external layer is several tens of micrometers in thickness. This layer is thus not eliminated during rough machining, but will permit a considerable increase of the rough machining quality. The wire obtained permits stabilizing the layer thus formed, which is accordingly no longer subject to degradation by the manganese with time. The invention also permits increasing the tensile strength of the covered wire because of the presence of manganese in the alloy. The electrode wires thus obtained can be stretched more greatly during machining and accordingly permit obtaining a better geometry on the cut piece and retard rupture of the wire while machining.
According to a preferred embodiment, the deposit is constituted by a binary alloy of manganese and zinc, the proportion of manganese being comprised between 5 and 85%, preferably between 10 and 60% and more preferably between 15 and 40% by weight.
This cladding alloy permits the particularly favorable characteristics of machining performance, deformability, resistance to traction and stability with time.
Preferably, the core has a concentric structure with the copper center and a peripheral layer of brass supporting said deposit.
These characteristics permit very high machining speeds.
The invention also relates to a process for the production of an electro-erosion electrode and is characterized to this end by the fact that a wire or rod forming said core is treated in an electrolytic bath arranged to produce a simultaneous deposition of manganese and at least one second metal selected from the group comprising Zn, Co, Cu, Ag, Fe, Mo, Ni, Se, Sn, W. This process by electrolytic co-deposition permits rapid and precise production at a moderate cost.
Preferably, the electrolytic bath is arranged so as to produce simultaneous deposition of manganese and zinc having a manganese proportion comprised between 5 and 85% by weight, the duration of treatment being determined so as to attain a layer by electrolytic deposit thicker than 1 micrometer.
Preferably, said electrolytic bath is an aqueous solution having the following composition:
monohydrated manganese sulfate in a concentration between 20 and 120 g/l, preferably 30 g/l;
hepta-hydrated zinc sulfate in a concentration between 50 and 80 g/l, preferably 65 g/l;
bi-hydrated sodium citrate in a concentration between 60 and 300 g/l, preferably 170 g/l.
With these characteristics there is obtained a very regular and stable cladding, whilst maintaining a moderate price.
Other advantages will become apparent from the characteristics set forth in the dependent claims and from the description of the invention given hereafter in greater detail with the help of drawings which show schematically and by way of example one embodiment.